Study of the coagulation-flocculation treatment of flowback water from shale gas hydraulic fracturing by using combination of dithiocarbamate compound-polyacrylamide.

In this paper, a dithiocarbamate-type flocculant DTC-TETA was prepared by using triethylenetetramine as the material and combination of DTC-TETA and polyacrylamide was used for the coagulation-flocculation of flowback water from shale gas hydraulic fracturing (FWSG). The coagulation-flocculation process was optimized by using turbidity as index and the recommended process was as follows: DTC-TETA dosage 200 mg/L, anionic polyacrylamide AN905 dosage 1 mg/L, flocculation stirring speed 200 rpm, flocculation stirring time 3 min and settlement time 5 min. The turbidity of FWSG can be reduced to be 13 NTU from the initial turbidity of more than 2000 NTU under the recommended process. The performance of DTC-TETA was much better than that of polyaluminum chloride and the Fe2+ in FWSG also can be removed. The function mechanism of DTC-TETA was investigated through the studies of zeta potential change of suspended solids and structural characteristics of flocs. The results confirmed that the flocs were developed by the network formed by the coordination reaction between DTC-TETA and Fe2+, which can filter out suspended solids. This study signifies that both suspended solids and Fe2+ ion can be removed by using DTC-TETA as flocculant, which is a new choice for the FWSG treatment. [ABSTRACT FROM AUTHOR]